Parallel Ribs Research Articles

Morphology and ultrastructure of cicatricose spores found in an isolated sporangium-bearing structure of a schizaealean fern from the Lower Cretaceous rocks at Casal do Borracho, Torres Vedras, western Portugal

Fossil spores provide important insights into the evolutionary history of ferns, including their morphological changes and adaptations over time. The morphology and ultrastructure of trilete spores with cicatricose sculpture composed of sets of parallel or near-parallel ribs (muri) have been studied. Observations on the spores were performed using light microscopy, scanning electron microscopy, and transmission electron microscopy. The cicatricose spores were extracted from a single sporangium-bearing structure collected from Casal do Borracho mesofossil flora near Torres Vedras (Lusitanian Basin, western Portugal) from sediments belonging to the Almargem Formation, considered to be of late Barremian or early Aptian age (and possible younger than that). The sporangium-bearing structure of a schizaealean fern and in situ cicatricose spores are compared with the family Anemiaceae. On the basis of spore size and shape, laesura length, with about 20 proximal narrow ribs, oriented perpendicular to the spore sides, and three sets of distal ribs forming V-shaped patterns, the cicatricose spores in the present study are clearly assigned to the fossil-taxon Cicatricosisporites venustus. The spore ultrastructure includes a homogeneous exospore of a blechnoid type with a slight difference in the thickness in the proximal, distal, and equatorial regions. The morphology and ultrastructure of the studied spores are corresponded to Anemia type.

Liquid-crystal clad tunable wavelength de-multiplexer and coupler/filter in silicon nitride rib waveguide structure

We report long-period waveguide grating (LPWG) based tunable wavelength de-multiplexer and tunable coupler/filter in liquid crystal (LC) clad rib waveguides on silicon nitride on insulator platform. High birefringence and electrically tunable refractive index of the MLC-9200-000 LC have been used to achieve a tuning range covering most of the S, C and L bands of the optical communication system. The structure consists of two parallel rib waveguides with an elevated slab. We have considered a new concept of injecting power into a higher-order slab mode. The power from the slab mode is coupled to the rib modes using LPWGs inscribed on the sidewalls of the ribs. The structure works as a tunable wavelength de-multiplexer when the grating periods in both ribs are different. The wavelength tunability of the de-multiplexer is achieved by an external voltage applied across the liquid crystal cell. Our numerical results show wavelength tuning of the de-multiplexer in the range 1.437 - 1.627 μm. The structure works as an electrically tunable coupler/filter when the grating period of both the gratings are the same. We numerically demonstrate the tuning of the coupler in the wavelength range 1.487 - 1.572 μm and that of the filter in the range 1.484 - 1.577 μm with 20-dB rejection.

A COMPARATIVE STUDY OF CHANNEL COOLING ENHANCEMENT BY ANGLED, PARALLEL BROKEN, AND RHOMBUS PATTERNED RIBS

Heating and cooling of fluids play an important role in energy engineering, such as solar air heaters and the internal cooling of gas turbine blades. Heat transfer in the heat exchanger channels can be enhanced by ribs, which will also result in a significant decrease in coolant pressure. In our previous work, a novel bioinspired rib design with a rhombus-shaped pattern was proposed to enhance the channel cooling. The Nusselt numbers and flow characteristics are further compared to angled and parallel broken ribs in this work. It is interesting to find that the proposed channel with decreasing-height rhombus-shaped patterned ribs exhibits the best heat transfer performance. At the same time, the Nusselt number and friction factor are related to the Reynolds number in the studied range. The surface with rhombus-shaped patterned ribs shows greater thermal performance factors than that with angled ribs, while the surface with a decreasing-height rib arrangement has the highest thermal performance factor due to a better Coanda effect. This work confirms that the proposed ribs with decreasing height rhombus-shaped patterns are effective for enhancing the internal cooling of the channel.

Effect of the number of ribbed walls on the thermal performance in rectangular channels with 45-deg parallel or criss-cross ribs

Regionally averaged heat transfer distributions and friction characteristics are experimentally investigated for fully developed, turbulent flow in a rectangular channel with a width-to-height aspect ratio (AR=3). 45-deg angled rib turbulators are placed on one, two, and four sides of the channel in parallel and criss-cross configurations with a pitch-to-height ratio(P/e=10) and a rib blockage ratio(eDh=4.1%). For a roughness Reynolds number range(e+=25−500), results show that increasing the number of ribbed walls improves the overall channel heat transfer for the 45-deg parallel ribs. Results reveal that four-sided ribbed channels provided the greatest thermal performance followed by the two-sided and one-sided ribbed channels, respectively, for both angled rib designs. On the basis of the law of wall similarity, friction and heat transfer roughness functions are derived using the four-sided data reported in this work. Furthmore, friction factors and heat transfer coefficients of similar angled rib designs were obtained from open literature and similarly correlated to derive more robust friction and heat transfer correlations over the roughness Reynolds number range. Thermal designers can use these proposed correlations to predict friction and heat transfer in rectangular cooling channels (AR=1-5) with various numbers of ribbed walls. The measured friction factor and heat transfer coefficient of this study can be predicted using these semi-empirical correlations with maximum errors of 9% and 7%, respectively.

Record of two rare taxa from Synura genus (Chrysophyceae) with a description of a new species (Synura tiksiensis sp. nov.) near the arctic settlement of Tiksi, Yakutia, Russia

A new species Synura tiksiensis (section Petersenianae) is described based on structure of silica scales, observed by scanning and transmission electron microscopy. The new species was recovered from several ponds near the arctic settlement of Tiksi (Yakutia, Russia). Synura tiksiensis scales have a narrow keel with large pores, ending with an acute, round tip, and rounded struts with big pores connected to each other by a parallel rib. Two rare species were found in one of the studied ponds: Synura petersenii f. taymyrensis and S. obesa. The latter was discovered for the first time after the initial finding. The species reassembles S. tiksiensis in scale structure. Described Synura species were found at water temperatures between 14.6–16.7 °C and pH 7.22–7.51.

Large displacement analysis of stiffened plates with parallel ribs under lateral pressure using FE modeling with shell elements

This study provides the load–displacement behavior of stiffened plates with parallel ribs when modeled using shell elements with and without considering the large-displacement effects in comparison with the conventional equivalent beam analysis (EBA) in which such stiffened plates are simplified into an imaginary beam with the geometrical properties of an equivalent built-up cross-section. This study highlights the advantages of FE modeling with shell elements and large-displacement analysis (LDA) over the existing EBA method and then provides a path for using this method in the ultimate limit state (ULS) design of stiffened plates. The stress distributions in the panel plate part of the stiffened plates are presented to demonstrate the significance of considering the large-displacement effects in the analysis. The numerical investigation indicated that the linear beam theory does not correctly presume the true behavior of the stiffened plates and that the corresponding load–displacement estimation does not align with its behavior predicted by the LDA. The results also demonstrate that when shell element modeling is utilized, the internal forces and stresses in the panel plate are calculated correctly, only if the large-displacement effects are considered in the analysis. Finally, a method for estimating the ultimate load capacity of stiffened plates with parallel ribs is provided, based on the large-displacement FE analysis with shell elements, which can be used to establish empirical design equations.

Thermal analysis of interaction between buoyancy induced flow under parallel rotation and rib induced vortices: Experimental and numerical study

This paper performing both experimental and numerical approaches underlines the aiding and opposing effects of secondary vortices resulting from parallel mode rotation on convective heat transfer coefficient in a rectangular channel in smooth and rib roughened channels. The Nusselt number is obtained by measuring the wall and fluid temperature at the Reynolds number ranging from 5118 to 10,677 and 0.07<Δρ/ρ<0.42. In addition, the Nusselt number is investigated in ribbed channels with one wall being perpendicularly ribbed at pitch ratio (P/e) and blockage ratio (e/Dh) equal to 15 and 0.088, respectively. Numerical simulations also allow to consider the effects of rotational induced secondary flows caused by centrifugal and the Coriolis forces in high rotation numbers (0<Ro<0.56) and Buoyancy numbers (0<Buo<1). The numerical results with non Boussinesq approximation for density variation show good agreement with experimental results, while it is revealed that the Nusselt number is underestimated if Boussinesq approximation is used. As the Reynolds number increases, the larger Buoyancy number is required to affect the Nusselt number. That is, under certain conditions which is expressed in terms of GrΩα/Re the rotational buoyancy effects may be negligible and the Nusselt number is equal to stationary case. However, in rib roughened channels the rotational buoyancy causes the reattachment point to occur closer to upstream rib while physical presence of ribs reduce the enhancing effects of rotation. Thus, for practical use in rotating cooling systems such as turbo-generators or electrical machinery, rib roughened channels are not recommended.

Flow and Heat Transfer Performance of Channels with ‎‎45 Degree Ribs in Staggered Array‎

The cooling efficiency of blade is growing demand with increasing turbine inlet temperature in gas ‎turbine development. Ribs used in cooling channels is a common cooling structure, therefore, many ‎configurations were studied by previous literatures, including angle, spacing, shape etc. However, there ‎are less research about the dislocation ribs structure. In this paper, the 45-deg parallel ribs, crossed ribs ‎and dislocation ribs were investigated by numerical simulation, in order to reveal the heat transfer ‎performance and flow mechanism. Refer to the experiment, SST k-ω model was applied in steady ‎simulation, at Re from 20000 to 50000. Due to the angled ribs can induce the secondary flow and ‎generate small helical vortices at front corner, heat transfer performance was elevated. The large rotating ‎vortices influenced by the ribs arrangement occupy the center channel, thence the dislocation caused ‎different flow and heat transfer results. The results shown that parallel rib has higher heat transfer ‎enhancement than crossed ribs, but pressure loss possess considerable level. At Re=21587, the averaged ‎turbulent kinetic energy of Case2.2 with dislocation ribs is 22.4% lower than parallel ribs. The all 45-deg ‎crossed ribs present higher level of overall thermal performance, and Case2.2 is optimal for the range of ‎Re investigated‎.

Study of Bond Strength of Plain Surface Wave Type Configuration Rebars with Concrete: A Comparative Study

This study investigates the bond strength behaviour of plain surface wave type configuration (PSWC) rebars in comparison to mild steel (MS) and high yield strength deformed (HYSD) rebars of varied rib configuration as per BIS and ASTM standards. The variables in the rebar include plain surface, curved surface, parallel rib, diamond rib and Nano modified cement polymer anticorrosive coating (CPAC). Total of 30 pull-out specimens and 12 beam-end specimens were put to a pull-out test following BIS and ASTM standard respectively. The load corresponding to 0.025mm free end (FE) slip and 0.25mm loaded end (LE) slip were carefully observed. The load-deflection behaviour, appearance of the first crack in the specimens and ultimate failure load was recorded. The experimental results showed that as compared to MS rebars, HYSD rebars offer an approximately threefold increase in ultimate bond strength and 1.5 times increase in usable bond strength irrespective of varied rib configuration. PSWC rebars with 4mm offset and 80mm pitch offered 2.4 times increase in ultimate strength and 76.2% increase in usable bond strength as compared to MS rebars. The ultimate pull-out load of PSWC rebars was around 25% and the usable bond strength was only 8.6% lesser than HYSD rebars with parallel ribs. The adopted coating enhanced the corrosion resistance and the reduction in bond strength with any surface configuration was less than the permissible maximum reduction of 20% as specified in IS 13620-1993. Hence it can be concluded that PSWC rebars offered promising bond strength results and upon further optimization and study in other aspects, PSWC rebars can be a way to replace HYSD rebars in future for enhancing concrete durability at zero added cost.

Experimental Study on the Influence of Film Cooling Hole Extraction on Heat Transfer and Flow Field in Internal Ribbed Cooling Channels of Turbine Blades

Abstract Film cooling and internal passage cooling play a fundamental role in turbine blade cooling. As the cooling holes are fed by the internal crossflow, interaction of these both cooling strategies is implicated. The influence of film hole extraction on the internal flow field and heat transfer of a ribbed cooling channel is investigated in this study. Therefore, a rectangular cooling channel (AR = 2:1) is equipped with parallel ribs of four different geometries (90 deg ribs, 60 deg ribs, 60 deg V-shaped ribs, and 60 deg Λ-shaped ribs) and also with bleed holes at varying positions between the ribs. The different geometrical configurations are examined using 2D-particle image velocimetry (PIV) for flow measurements and transient thermochromic liquid crystal (TLC) technique for heat transfer measurements. Depending on the rib-induced heat transfer pattern, cooling hole positions in the rib segments are found, which can enhance passage internal heat transfer. 90 deg and 60 deg ribs show the best results for upstream hole positions regardless of the lateral positioning. V and Λ ribs reveal a benefit for lateral positioned cooling holes near the upstream rib.

Multi-objective design optimization of variable ribs composite grid plates

Grid structures are among the most lightweight elements for stiffening the plates and shells or as self-sufficient structures. There are different known grid patterns, which are composed of variable numbers of parallel ribs. Selecting an optimum pattern and geometries for a grid to achieve the minimum weight and maximum load-bearing capacity is a challenging procedure for designers. In the current study, a variable ribs model (VRM) is proposed to find the optimum architecture of a grid plate. Therefore, using a genetic algorithm process, a multi-objective optimization is implemented to maximize the axial or shear buckling loads at a minimum possible weight of a grid structure. Eleven geometrical parameters including thickness, width, and the number of ribs as well as the orientation of the grid plate are considered the design variables. The multi-objective optimization is carried out employing the e-constraint method. The buckling loads are obtained based on the first-order shear deformation plate theory using the Ritz method.

The Influence of Rib Configuration on Bond Strength Development between Steel and Concrete

The bond strength between rebar and concrete is important for the quality performance of reinforced concrete structures. At the interface, bond strength development mainly depends on surface configuration. Different rib configuration improves the strength significantly in high yield rebars as compared to mild steel. This study examines the bond strength behavior of ordinary MS (Mild Steel) rebars, HYSD (High Yield Strength Deformed) parallel rib, and HYSD diamond rib rebars. Experimental analysis to obtain pull-out behavior of rebar in concrete was based on IS 2770 Part I – 1967: Reaffirmed 2007; Indian Standard Methods of Testing Bond in Reinforced Concrete. Importantly, the concrete of M30 grade was used and a total of nine specimens were tested. The cubes of size 150mm x 150mm x 150mm were cast with centrally embedded rebar provided up to 20 mm from their bottom faces. Additionally, the pull-out test was conducted in 1000 kN capacity Universal Testing Machine. The usable bond strength values were calculated from the load at 0.025 mm free and 0.25 mm loaded end slips. The results showed that the usable bond strength value of HYSD diamond rib rebars is very large compared to MS and appreciably greater than HYSD parallel rib. Moreover, the usable bond strength of HYSD diamond rib rebars is 60.06% and 35.60 % greater than that of the MS rebars and HYSD parallel rib pattern rebars, respectively. The high frictional resistance developed in the bond strength test of HYSD diamond rib rebars because of the better mechanical interlocking. This was primarily due to the presence of a more frictional surface area of lugs.

Turning Guide Vane Effect on Internal Cooling of Two-Passage Channel With Parallel Ribs

Abstract The present work investigates the effects of various guide vane designs on the heat transfer enhancement of rotating U-duct configuration with parallel 45-deg ribs. The ribs were installed on the bottom wall of the channel, which has a constant heat flux boundary condition. The channel has a square cross section with a 5.08 cm hydraulic diameter. The first and second passes are 514 mm and 460 mm, respectively. The range of Reynolds number for turbulent flow is up to 35,000. The channel rotates at various speeds up to 600 rpm, which brings the maximum rotation number of 0.75. Several computational fluid dynamics simulations are carried out for this study to understand the effect of guide vanes on flow and heat transfer in serpentine channels under various operating conditions.

Formation of nanoripples on ZnO flat substrates and nanorods by gas cluster ion bombardment.

In the present study Ar+ cluster ions accelerated by voltages in the range of 5–10 kV are used to irradiate single crystal ZnO substrates and nanorods to fabricate self-assembled surface nanoripple arrays. The ripple formation is observed when the incidence angle of the cluster beam is in the range of 30–70°. The influence of incidence angle, accelerating voltage, and fluence on the ripple formation is studied. Wavelength and height of the nanoripples increase with increasing accelerating voltage and fluence for both targets. The nanoripples formed on the flat substrates remind of aeolian sand ripples. The ripples formed at high ion fluences on the nanorod facets resemble well-ordered parallel steps or ribs. The more ordered ripple formation on nanorods can be associated with the confinement of the nanorod facets in comparison with the quasi-infinite surface of the flat substrates.

Experimental Study on the Influence of the Streamwise Position of Film Hole Extraction in Internal Ribbed Cooling Channels of Turbine Blades

The concurrent use of film cooling and internal cooling plays an important role to maintain the life of turbine blades and increase thermal efficiency. Several studies were published on the interaction of these cooling strategies but these are mainly investigations on how internal cooling influences film cooling. The present study contributes to an improved understanding on how the cooling extraction through film cooling holes is influencing internal flow structures and therefore internal cooling. The flow field in an internal cooling channel is investigated by measuring the velocity distribution with 2D-PIV. Heat transfer measurements are performed using the thermochromic liquid crystal technique. The test stand models a rectangular cooling channel (AR=2:1), which is equipped with parallel ribs of four different geometries (90° ribs, 60° ribs, 60°-V-shaped ribs and 60°-Λ-shaped ribs). Bleed holes are placed in the rib segments and are positioned at three positions in streamwise direction. The suction ratio is varied between 0 and 6 and the cooling channel Reynolds number is 30.000.

Reinterpretation of fossil reproductive structures Zlivifructus microtriasseris (Normapolles complex, Fagales) from the Czech and Polish Late Cretaceous

Flowers and fruits of Zlivifructus microtriasseris, originally described as Caryanthus microtriasseris from the late Turonian to Santonian of the South Bohemian Basins and the late Coniacian to early Santonian of the North Sudetic Basin, are reinterpreted here. Zlivifructus microtriasseris is represented by small, flat fruits, round in outline with persistent perianths, which are fused basally, forming the hypanthium. The hypanthium extends for more than two-thirds of the fruit. Tepals leave scars indicating their insertion. Lateral attachment scars of tepals and medial attachment scars are immediately adjacent to each other, with indistinct boundaries forming a ring. The androecium consists of four stamens.The fruit shows the unilocular nature of the nut with a single seed. Lateral faces of the fruit show two parallel ribs or ridges, running from the base of the fruit to the margin of the hypanthium. The surface of the fruit bears irregularly shaped cells. Zlivifructus microtriasseris differs from species assigned to genus Caryanthus Friis 1983 in the presence of four stamen scars, and in having two lateral ribs in the face of the fruit. Zlivifructus microtriasseris differs from the type species Zlivifructus vachae in size of the fruit; shape of the fruit; perianth and attachment scars of tepals. A probabilistic classification method to differentiate between the two fruit species based on their size is proposed.

OPTIMIZATIONAL TRACTION TASKS ON THE RAILWAY NETWORK

Purpose. The paper involves the development of information and algorithmic support for conducting the optimization traction and energy calculations on the railway network for their further use in decision-making systems – systems for efficient management of the transport process. Methodology. The system is based on the graph-analytic system, the model of the train with different types of traction, the methods of optimal control of the train and the fundamental algorithms on the weighted graphs with possible parallel ribs (arcs). In the complex, these components of the system provide finding the tracks on the chart-diagram according to the given criteria, conducting the optimization traction-energy calculations according to different criteria, as well as conducting a comparative analysis of the obtained results. The reliability of the results has been repeatedly checked by available methods for varying complexity of race according to the plan and profile of the course. For this purpose, data obtained as a result of control visits using dynamometric cars were used. Also a comparative analysis of the modes in operation of trains, calculated and received by qualified drivers on different races was conducted. Findings. The problem of efficient operation of various types and modifications of locomotives, involved in the implementation of trains schedules for different purposes and loads is considered. Presentations of direct and inverse optimization, according to various criteria, of the regime tasks on the railway network and variants of their effective solution are given. The analysis of the results of the developed mathematical support and the ideas of implemented algorithms is given. Originality. The paper proposes the establishment of the network optimization problems that arise at the stages of the developing the plan for the formation, construction of traffic schedules, transmission capacity assessment and the calculation of optimal parameters for the composite graphs of motion, etc. The system approach is important to ensure the combination of the developed network structure in the universal terms of the graph theory with the system of actualization of their parameters. Pull and energy efficiency calculations are carried out by combinatorial optimization methods, which ensured the maximum level of automation of the process in solving a large set of direct and inverse regime problems with different optimality criteria. Practical value. The information and algorithmic support for the automation of the process in solving the direct and reverse regime traction-energy problems on the railway network was developed. It was tested in the process of calculating the main components for the formation of traffic schedules, analysis of train driving modes, assessment in choosing the optimal parameters of the track reconstruction for high-speed and new types of trains (locomotives).

Heat Transfer in a Rotating Cooling Channel (AR = 2:1) With Rib Turbulators and a Tip Turning Vane

Experimental investigation on rotation and turning vane effects on heat transfer was performed in a two-pass rectangular internal cooling channel. The channel has an aspect ratio of AR = 2:1 and a 180 deg tip-turn, which is a scaled up model of a typical internal cooling passage of gas turbine airfoils. The leading surface (LS) and trailing surface (TS) are roughened with 45 deg angled parallel ribs (staggered P/e = 8, e/Dh = 0.1). Tests were performed in a pressurized vessel (570 kPa) where higher rotation numbers (Ro) can be achieved with a maximum Ro = 0.42. Five Reynolds numbers (Re) were examined (Re = 10,000–40,000). At each Reynolds number, five rotational speeds (Ω = 0–400 rpm) were considered. Results showed that rotation effects are stronger in the tip regions as compared to other surfaces. Heat transfer enhancement up to four times was observed on the tip wall at the highest rotation number. However, heat transfer enhancement is reduced to about 1.5 times with the presence of a tip turning vane at the highest rotation number. Generally, the tip turning vane reduces the effects of rotation, especially in the turn portion.

On-orbit space camera self-calibration based on the orthogonal vanishing points obtained from solar panels

As one of the key steps of machine visual investigation, camera calibration is indispensable for obtaining an accurate 3D profile of measured objects and positioning the target. However, it is almost impossible to calibrate a camera on-orbit in real time, for the feature points in space are irregular. To self-calibrate camera parameters in orbit, we propose a method to calibrate the camera using the orthogonal vanishing points obtained from a solar panel, which is a common component of most man-made space satellites. Using two sets of images of orthogonal parallel ribs of a solar panel under any two positions, four vanishing points are achieved. Based on the geometrical property of the orthogonal vanishing point and the infinite homography relationship between the corresponding vanishing points under different camera positions, a camera self-calibration method is proposed, and constraint equations are established to calibrate the intrinsic parameters of the camera linearly. Aiming at restraining the influence of the noise on the calibration result, an objective function based on the inverse point characteristics of rectangular imaging is proposed, and the Levenberg–Marquardt optimization algorithm is used to nonlinearly optimize the intrinsic parameters. Simulated and experimental results show that the 2D reprojection error is 0.86 pixels. This method, therefore, has better applicability in some significant space and national defense missions, such as space rendezvous and docking, attack-defense, and on-orbit servicing. The optimization algorithm shows good anti-noise interference performance, therefore the robustness of the calibration algorithm is improved.

리브가 있는 확대 사각 채널에서 국부 열전달

The local heat transfer of developed turbulent flows in the stationary ribbed divergent rectangular channels has been experimentally checked out. The rectangular divergent channels with the outlet hydraulic diameter(Dho) to inlet hydraulic diameter(Dhi) ratio of 1.49 have one-sided ribbed wall or two-sided ribbed walls, at which the ribbed walls with the flow attack angle of 60o are manufactured with a fixed rib height(e)=10 mm and the ratio of rib spacing(P) to rib height(e)=10. The measurements of heat transfer for V-shaped continuous ribs(case A), parallel broken ribs(case B), and V-shaped broken ribs(case C) have been conducted within the range of Re from 22,000 to 72,000.BR The comparison indicates that among the three different rib arrangements of case A, case B, and case C with two ribbed walls, the case A has the greatest Nusselt number, at which case A and case C produce 158% and 122 higher than case B at Re of 54,000.